The present invention relates to apparatus for testing materials and more particularly to a testing machine which measures the changes occurring at a test specimen when subjected to a load at elevated temperatures and pressures.
Testing machines utilized for determining the characteristics of material specimens are well known and generally comprise apparatus for mounting the specimen in a piece of apparatus which is adapted to subject the specimen to tensional, compressional or torsional loads and measuring the dimensional changes, for example, as the load is applied under controlled conditions. More recently, it has become desirable to make such measurements within a particular type of controlled environment such as elevated temperature and/or pressure. Such apparatus requires that the specimen be placed in a closed container or housing which is capable of withstanding the conditions to which the specimen is being subjected. The loading forces which are to be applied to the specimen are externally generated, for example, by means of a piston type actuator which is coupled to the specimen through a pull rod passing into the housing through a set of seals. Additionally, measuring devices such as load cells and linear variable differential transformers are included for measuring the desired parameters during a testing procedure.
With respect to known prior art, U.S. Pat. No. 4,018,080, Fletcher, et al., entitled, "Device For Tensioning Test Specimens Within A Hermetically Sealed Chamber", for example, discloses a load cell in series with a piston located above a high temperature chamber with the piston applying a load to the specimen located within the chamber. In U.S. Pat. No. 4,019,365, Woo, entitled, "Thermo Chemical Analyzer", there is disclosed a linear variable differential transformer in series with a load column, with the load column being coupled to a test specimen mounted in a temperature chamber. The linear variable differential transformer, moreover, is mounted above the temperature chamber. Other examples of linear variable differential transformers are included in the teachings of U.S. Pat. No. 3,234,778, Kreglo, entitled, "Diletometer For Heated Specimens Under External Stress", and U.S. Pat. No. 3,028,754, Huyser, entitled, "Measurement Instrument".
While such apparatus is presumed to operate in the manner intended, certain limitations nevertheless exist, for example, the pull rod coupled between the specimen and actuator generating the load forces is often subjected to a condition where a pressure generated force tending to eject the pull rod is generated within the housing containing the specimen
Present technology requires removal of the load cell, lifting the pull rod almost completely out of the housing, and assembling the new specimen to both the housing cover and the pull rod prior to reinsertion of the pull rod. This action imposes large displacement of the pull rod relative to the seals. Since non-wiped areas are involved, the seals are subjected to abrasive action tending to shorten their lifetime.